Water-blown polyurethane integral skin foam

ABSTRACT

The invention relates to water blown integral skin polyurethane foams made with a particular isocyanate quasi-prepolymer and resin side ingredients to yield a foam having good overall mechanical properties. The isocyanate quasi-prepolymer component of the present invention comprises from 0.5 weight percent to 30.0 weight percent or less uretonimine-carbodiimide-modified diphenylmethane diisocyanate, from 50 weight percent to 80 weight percent 4,4&#39;-diphenylmethane diisocyanate and reacted with from 15 weight percent to 40 weight percent of a polyether polyol containing predominately secondary hydroxyl groups and having an average molecular weight from about 2,000 to 10,000, an average functionality from 1.5 to about 3.2, and a hydroxyl number from about 20 to 60, and optionally with a low molecular weight diol in an amount of from 1.0 weight percent to 10 weight percent, the weight percentages based on the weight of the quasi-prepolymer reactants. The resin side component comprises a high molecular weight polyether compound having isocyanate reactive hydrogens and average molecular weights from about 2,000 to about 10,000 and an average functionality from 1.5 to about 3.2, water as a blowing agent in an amount of from 0.25 weight percent to 3 weight percent, an effective amount of polyurethane and/or polyurea promoting catalyst, a surfactant, and a chain extender, and optionally a mono- or di- functional alcohol composition having from 8 to about 30 carbon atoms. 
     The components, when injected or poured into a preheated mold, can tolerate mold temperatures from 105° F. to 135° F. and can be demolded in less than 150 seconds to yield an integral skin foam having little or no bubbles or pores visible to the eye. The foam produced thereby has a compression set of 30 percent or less, high tensile strength, and high tear strength.

This is a division of application Ser. No. 08/048,444 filed Apr. 15,1993 pending.

The present invention relates to water-blown polyurethane integral skinfoams and elastomers, more particularly to water-blown polyurethaneintegral skin foams having low compression set, good mechanicalproperties, and good processing characteristics, especially for use assteering wheels.

BACKGROUND OF THE INVENTION

It is generally known that polyurethane foams can be manufactured usingwater as a blowing agent. The reaction of an isocyanate group with wateryields an urea group and evolves carbon dioxide gas, acting as the agentresponsible for the foaming action. The presence of urea groups,however, hardens the foam and leads to poor compression set values. Inresponse to this problem, polyphenylene polymethylene polyisocyanate(polymeric-MDI) has been added to improve compression set; but theimprovement has come at the expense of other physical properties, suchas elongation, tear strength, and tensile strength. Therefore, theinventors herein have sought to make a water-blown polyurethane integralskin foam which simultaneously possesses good compression set,elongation, tear strength, and tensile strength comparable to aCFC-blown integral skin polyurethane foam, and to formulate a systemthat processes well, is not sensitive to minor processing conditions,and demolds quickly.

SUMMARY OF THE INVENTION

It is an object of the invention to make a polyurethane integral skinfoam blown with water as a replacement for chlorofluorocarbon-blownpolyurethane integral skin foams. The water-blown foam mustsimultaneously possess good mechanical properties, compression set, andother mechanical properties, especially tear strength, tensile strength,and elongation.

It is a further object of the invention to make a water-blown integralskin polyurethane foam having good processing characteristics, namely,low demold times, higher limitation mold temperatures, and wideprocessing windows to allow for larger margins of error in formulationand processing conditions.

It has now been discovered that a particular isocyanate quasi-prepolymerwhen reacted with particular resin side ingredients yields a water-blownintegral skin foam having good overall mechanical properties. Theisocyanate quasi-prepolymer component of the present invention comprisesfrom 0.5 weight percent to 30.0 weight percent, preferably from 0.5 toless than 12.5 weight percent uretonimine-carbodiimide-modifieddiphenylmethane diisocyanate, from 50 weight percent to 80 weightpercent 4,4'-diphenylmethane diisocyanate; reacted with from 15 weightpercent to 40 weight percent of a polyether polyol containingpredominately secondary hydroxyl groups and having an average molecularweight from about 2,000 to 10,000, an average functionality from 1.5 toabout 3.2, and a hydroxyl number from about 20 to 60, and optionallywith a low molecular weight diol in an amount of from 1.0 weight percentto 10 weight percent, the weight percentages based on the weight of thequasi-prepolymer reactants. The quasi-prepolymer may optionally be mixedwith 1 weight percent to 30 weight percent polyphenylene polymethylenepolyisocyanate as a blend of quasi-prepolymer/polymeric MDI. The resinside component comprises a high molecular weight polyether compoundhaving isocyanate reactive hydrogens and average molecular weights fromabout 2,000 to about 10,000 and an average functionality from 1.5 toabout 3.2, water as a blowing agent, an effective amount of polyurethaneand/or polyurea promoting catalyst, a surfactant, and a chain extender,and optionally a mono- or di- functional alcohol composition having from8 to about 30 carbon atoms.

The components, when injected or poured into a preheated mold, cantolerate mold temperatures from 105° F. to 135° F., preferably 115° F.to 135° F. and can be demolded in less than 150 seconds to yield anintegral skin foam having little or no bubbles or pores visible to theeye. The process is not particular to a narrow range of moldtemperatures, does not require a large number of vent holes, and istolerant of a wide range in component temperatures spanning from 75° F.to 95° F.

DETAILED DESCRIPTION OF THE INVENTION

The integral skin foams produced in this invention are flexible and haveoverall molded densities ranging from 20 pcf to 40 pcf. Applications ofthe foam include automotive parts such as steering wheels, armrests,horn covers, headrests, or trim and non-automotive applications such asshoe soles, gaskets, or furniture parts.

The Quasi-prepolymer Component

The isocyanate quasi-prepolymer of the invention is prepared by reactinga mixture or blend of 4,4'-diphenylmethane diisocyanate (4,4'-MDI) anduretonimine-carbodiimide-modified 4,4'-diphenylmethane diisocyanate witha composition bearing isocyanate reactive hydrogens.

The carbodiimide modification of 4,4'-MDI can be represented by theformulas: ##STR1## This carbodiimide then reacts predominately withfurther unconverted 4,4'-MDI to form uretonimine-modified 4,4'-MDIrepresented by the following formula: ##STR2##

The uretonimine-carbodiimide-modified polyisocyanate is obtained byemploying well-known carbodiimide-promoting catalysts in thepolyisocyanate to convert the isocyanate to the carbodiimide attemperatures from 50° C. to 250° C., which then proceeds to react withfurther unconverted polyisocyanates at room temperature to form auretonimine-modified polyisocyanate. The polyisocyanate employed in theconversion to carbodiimide and uretonimine is 4,4'-MDI. The extent towhich the carbodiimide modification is further converted to theuretonimine form varies with the reaction temperature and the time inwhich the reaction mixture is allowed to stand at room temperature.However, as employed in the invention, a"uretonimine-carbodiimide-modified 4,4'-MDI" is one which contains auretonimine/carbodiimide ratio greater than 50:50, preferably a ratioranging from 85-99:15-1 by weight. Although a 100 weight percenturetonimine-modified 4,4'-MDI may be employed, the conversion fromcarbodiimide to uretonimine does not usually go to completion; and therenormally remains some carbodiimide present in the MDI. Typical catalystsuseful in the conversion of a diisocyanate to carbodiimide-modifieddiisocyanate include phospholene 1-oxides and 1-sulfides, diaza- andaxaza-phospholanes and phosphorinanes, triaryl arsines, and trialkylphosphates as described in U.S. Pat. No. 4,743,626, herein incorporatedby reference.

During the process of making the uretonimine-carbodiimide-modified MDI,it is preferred that about 5 weight percent to 35 weight percent, morepreferably from 20 weight percent to 30 weight percent of the MDI isconverted to the uretonimine-carbodiimide form. The MDI compositioncontaining the uretonimine-carbodiimide-modified MDI is preferablyblended with further MDI prior to reaction with the polyether polyol toyield the desired quasi-prepolymer, or the conversion touretonimine-carbodiimide MDI may take place in the total amount of MDIdesired prior to reacting with polyol, thereby eliminating the need toblend with further MDI. The amount of uretonimine-carbodiimide-modifiedMDI present in the quasi-prepolymer is from 0.5 weight percent to 30weight percent, preferably from 0.5 to less than 12.5 weight percent,more preferably from 1.0 weight percent to 7.0 weight percent, based onthe weight of all ingredients in the quasi-prepolymer. An alternativeembodiment uses from 3 weight percent to 12.5 weight percent ofuretonimine-carbodiimide-modified MDI.

The MDI utilized in the invention comprises 4,4'-MDI, 2,4'-MDI,2,2'-MDI, or mixtures of these isomers. The amount of 4,4'-MDI isomer inthe quasi-prepolymer is from 50 weight percent to 80 weight percent,preferably from 65 weight percent to 75 weight percent, most preferablyabout 70 weight percent, based on the weight of all ingredients in thequasi-prepolymer. The amount of 2,4'-MDI and 2,2'-MDI isomers isadvantageously less than 4 weight percent, more preferably less than 1weight percent of the quasi-prepolymer. Thus, the MDI in thequasi-prepolymer is essentially 4,4'-MDI.

The remaining portion of the quasi-prepolymer comprises a high molecularweight polyether polyol composition in an amount of from 15 weightpercent to 40 weight percent of the quasi-prepolymer, preferably in anamount of from 20 weight percent to 30 weight percent. The polyetherpolyol has a high average molecular weight ranging from 2,000 to 10,000,preferably from 2,500 to 5,000, has an average functionality from 1.50to 3.2, and a hydroxyl number from 20 to 60. Since a water-blownpolyurethane foam produces hard urea segments, it has been found that itis necessary to employ high molecular weight polyether polyols to softenup the polyurethane polymer.

The polyether polyol composition of the invention contains a predominantamount of secondary hydroxyl groups, with a composition consisting ofall secondary hydroxyl groups being preferred. By a predominant amountof secondary hydroxyl group containing polyether polyol composition, itis meant that no more than about 3.5 weight percent of the polyetherpolyol should be terminated with polyoxyethylene groups or groupsproducing primary hydroxyl termination. It is acceptable to add ethyleneoxide to prepare a heteric or internal block polyether polyol so long asno more than 3.5 weight percent of the polyol is terminated with primaryhydroxyl groups. Although it is within the scope of the invention to addthe above minor amounts of ethylene oxide to an initiator molecule as acap, it is preferable to prepare a polyoxyalkylene polyether polyolexclusively containing secondary hydroxyl groups. It is believed thatthe tear strength, compression set, and tensile strength of the moldedarticle tend to degrade when more than minor amounts of ethylene oxideas a cap are added in the preparation of the polyether polyol used inthe formation of the quasi-prepolymer. Thus, a polyether polyol preparedby oxypropylating an initiator molecule without addition of any ethyleneoxide yields a prepolymer, which when used in the resin described below,produces an integral skin foam having optimal mechanical properties.

Methods of making polyether polyols are well known and include thosepolyethers prepared from the base catalyzed addition of an alkyleneoxide such as propylene oxide or butylene oxide, preferably propyleneoxide, to an initiator molecule containing, on the average, two or moreactive hydrogens. The polyoxyalkylene polyether polyols may be preparedby any known process such as, for example, the process disclosed byWurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp257-262, published by Interscience Publishers, Inc. (1951) or in U.S.Pat. No. 1,922,459, hereby incorporated by reference. Examples ofinitiator molecules are diethylene glycol, ethylene glycol, dipropyleneglycol, propylene glycol, trimethylene glycol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,4-pentanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, glycerine, 1,1,1-trimethylolpropane,1,1,1-trimethylolethane, 1,2,6-hexanetriol, or triethylolpropane.Particularly preferred initiators include trimethylolpropane, propyleneglycol, and blends of polyoxyalkylene polyether polyols initiatedthereby, with propylene glycol being most preferred.

Suitable alkylene oxides propylene oxide, butylene oxide, amylene oxide,and mixtures of these oxides. Preferred is the reaction product of allpropylene oxide with one of the aforementioned initiators, preferablypropylene glycol, to yield a polyether polyol having only secondaryhydroxyl groups. In one embodiment, the polyether polyol has a molecularweight from 3,000 to 3,600, an average functionality from about 1.7 to2.0, a hydroxyl number from 26 to 37, and prepared by adding propyleneoxide to a propylene glycol initiator.

Also suitable as the polyol are polymer-modified polyols, in particular,the so-called graft polyols in which the carrier polyol containssubstantially all secondary hydroxyl groups. Graft polyols are wellknown to the art and are prepared by the in situ polymerization of oneor more vinyl monomers, preferably acrylonitrile and styrene, in thepresence of a polyether or polyester polyol, particularly polyolscontaining a minor amount of natural or induced unsaturation. Methods ofpreparing such graft polyols may be found in columns 1-5 and in theExamples of U.S. Pat. No. 3,652,639; in columns 1-6 and the Examples ofU.S. Pat. No. 3,823,201; particularly in columns 2-8 and the Examples ofU.S. Pat. No. 4,690,956; and in U.S. Pat. No. 4,524,157, all of whichpatents are herein incorporated by reference.

The quasi-prepolymer is prepared over a one- to five-hour period at 50°C. to 80° C., preferably at 60° C. to 70° C., by introducing the desiredquantity of polyether polyol at a constant rate over about a one-hourperiod into a preheated reactor containing the desired quantity of MDIand uretonimine-carbodiimide-modified MDI. The reaction is carried outin the presence of a catalyst deactivator, at reaction temperatures orlower, and preferably in an inert gas atmosphere. The reaction ischecked after a period of time to determine the free NCO content, andheating is continued until the desired NCO content is attained. It ispreferable that the quasi-prepolymer has an NCO content of 10 to 32weight percent, more preferably from 20 to 30 weight percent, mostpreferably from 22 to 26 weight percent.

Suitable catalyst deactivators include salts such as magnesium chloridedihydrate, acid chlorides such as benzoyl chloride and acetyl chloride,acids such as hydrochloric acid, oxalic acid, phosphoric acid,benzenesulfonic acid, toluenesulfonic acid, methanesulfonic acid ortrifluoromethanesulfonic acid, sulfonyl chlorides such asbenzenesulfonyl chloride, toluenesulfonyl chloride, and the like. Otherdeactivators which may be employed are such agents as dimethylsulfate,alkyl o,p-toluenesulfonates, methylchloride and similar compounds asdisclosed in U.S. Pat. Nos. 3,769,318 and 4,738,991, each hereinincorporated by reference.

Another feature of the invention is the preparation of aquasi-prepolymer having increased viscosity and greater storagestability where the quasi-prepolymer is stable at 10° C. for two weeks.This is accomplished by blending a low molecular weight diol, triol, ortetrol of less than 175 in an amount of from 1.0 weight percent to 10weight percent, based on the weight of the quasi-prepolymer, with thepolyether polyol, and subsequently introducing the polyether polyol/diolblend into the reactor containing the MDI according to theaforementioned method of reaction. In addition, the storage stability isenhanced by increasing the levels of uretonimine-carbodiimide modified4,4'-MDI in the quasi-prepolymer. Suitable diols include dihydricinitiators employed in the preparation of the polyether polyol, withpreferable diol being dipropylene glycol and ethylene glycol. It is alsopreferable to add the low molecular weight diol to the MDI in an amountof from 4 weight percent to 6 weight percent. During the course of thereaction, the free NCO content and viscosity may be checked to determinewhether the desired target has been achieved, namely, an NCO content asdescribed above and an increased viscosity greater than about 200 cP,preferably greater than 275 cP.

An optional feature of the invention comprises blending polymeric-MDIwith the quasi-prepolymer to make a 1-30/70-99polymeric-MDI/quasi-prepolymer blend. The polymeric MDI containsapproximately 35 weight percent to 65 weight percent4,4'-diphenylmethane diisocyanate, 10 weight percent to 20 weightpercent three-ringed aromatic polyisocyanates, and 25 weight percent to45 weight percent higher functional oligomers. However, excellentmechanical properties such as compression set have been achieved in theabsence of any polymeric MDI reacted with or blended with thequasi-prepolymer.

The Resin Component

The resin side component comprises a blend of a composition havingisocyanate reactive hydrogens and of high molecular weight, water, oneor more polyurethane catalysts, a surfactant, a chain extender, andoptionally a mono-functional alcohol composition.

The composition having isocyanate reactive hydrogens has an averagemolecular weight of from 2,000 to 10,000, preferably 3,500 to 6,000,most preferably from about 4,000 to about 5,000, and an averagefunctionality from 1.5 to 3.2. Suitable compositions comprisepolyhydroxyl-containing polyesters, polyoxyalkylene polyether polyols,polyhydroxy-terminated polyurethane polymers, polyhydroxyl-containingphosphorus compounds, and alkylene oxide adducts of polyhydricsulfur-containing esters, polyacetals, aliphatic polyols or diols,ammonia, and amines including aromatic, aliphatic and heterocyclicamines as well as mixtures thereof. Alkylene oxide adducts of compoundswhich contain two or more different groups within the above-identifiedclasses may be used such as amino alcohols which contain an amino groupand a hydroxyl group. Also, alkylene oxide adducts of compounds whichcontain 1-SH group and one --OH group as well as those which contain anamino group and a --SH group may be used.

Any suitable hydroxy-terminated polyester may be used such as areobtained, for example, from polycarboxylic acids and polyhydricalcohols. Any suitable polycarboxylic acid may be used such as oxalicacid, malonic acid, succinic acid, glutaric acid, adipic acid, palmelicacid, suberic acid, azelaic acid, subacic acid, brassylic acid, thapsicacid, maleic acid, fumaric acid, glutaconic acid, alpha-hydromuconicacid, betahydromuconic acid, alpha-butyl-alpha-ethyl-glutaric acid,alpha, beta-diethylsuccinic acid, isophthalic acid, terephthaic acid,hemimellitic acid, and 1,4-cyclohexane dicarboxylic acid and mixturesthereof. Any suitable polyhydric alcohol may be used such as ethyleneglycol, propylene glycol, trimethylglycol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, glycerol,1,1,1-trimethylolpropane, 1,1,1-trimethylolethane, 1,2,6-hexanetriol,alphamethyl glucoside, pentaerythritol and sorbitol and mixturesthereof. Also included within the term "polyhydric alcohol: arecompounds derived from phenol such as 2,2-bis(4-hydroxyphenyl)propane,commonly known as Bisphenol A.

Any suitable polyoxyalkylene polyether polyol may be used as thepolymerization product of an alkylene oxide with a polyhydric alcohol.Any suitable polyhydric alcohol may be used such as those disclosedabove for use in the preparation of the hydroxy-terminated polyestersand for the preparation of the quasi-prepolymer. Any suitable alkyleneoxide may be used such as ethylene oxide, propylene oxide, butyleneoxide, amylene oxide, and mixtures of these oxides. The polyalkylenepolyether polyols may be prepared from other starting materials such astetrahydrofuran and alkylene oxide-tetrahydrofuran mixtures;epihalohydrins such as epichlorohydrin; as well as arylalkylene oxidessuch as styrene oxide. The polyalkylene polyether polyols may also haveeither primary or secondary hydroxyl groups.

Polyethers are preferred and preferably include the alkylene oxideaddition products of dipropylene glycol, trimethylolpropane, glycerine,propylene glycol, dipropylene glycol, and2,2-bis(4-hydroxyphenyl)propane and blends thereof having equivalentweight of from 100 to 5,000.

Suitable polyhydric polythiol ethers which may be condensed withalkylene oxides include the condensation product of thiodiglycol or thereaction product of a dicarboxylic acid such as is disclosed above forthe preparation of the hydroxyl-containing polyesters with any othersuitable thioether glycol.

The hydroxyl-containing polyester may also be a polyester amide such asis obtained by including some amine or amino alcohol in the reactantsfor the preparation of the polyesters. Thus, polyester amides may beobtained by condensing an amine alcohol such as ethanol amine with thepolycarboxylic acids set forth above or they may be made using the samecomponents that make up the hydroxyl-containing polyesters with only aproportion of the components being a diamine such as ethylenediamine.

Polyhydroxyl-containing phosphorous compounds which may be used includethose compounds disclosed in U.S. Pat. No. 3,639,542. Preferredpolyhydroxyl-containing phosphorous compounds are prepared from alkyleneoxides and acids of phosphorous compounds having a P₂ O₅ equivalency offrom about 72 percent to about 95 percent.

Suitable polyacetals which may be condensed with alkylene oxides includethe reaction product of formaldehyde or other suitable aldehyde with adihydric alcohol or an alkylene oxide such as those disclosed above.Suitable aliphatic thiols which may be condensed with alkylene oxidesinclude alkane thiols containing at least 2-SH groups as1,2-ethanedithiol, 1,2-propanedithiol, 1,3-propanedithiol, and1,6-hexanedithiol; alkane thiols such as 2-butene-1,4-dithiol; andalkane thiol such as 3-hexane-1,6-dithiol.

Suitable amines which may be condensed with alkylene oxides includearomatic amines such as aniline, o-chloroaniline, p-amino aniline,1,5-diaminonaphthalene, methylene dianiline, the condensation productsof aniline and formaldehyde, and diamino toluene; aliphatic amine suchas methylamine, tris-isopropanol amine, ethylene diamine,1,3-diaminopropane, 1,3-diaminobutane, and 1,4-diaminobutane.

The polyurethane foams of the present invention may also be prepared bythe reaction of a graft copolymer polyol with the quasi-prepolymer.Suitable graft copolymers are such as those described above in thepreparation of the quasi-prepolymer.

Chain extending agents employed in the preparation of the polyurethanefoams include those compounds having at least two functional groupsbearing active hydrogen atoms such as water, hydrozene, primary andsecondary diamines, amino alcohols, amino acids, hydroxy acids, glycolsor mixtures thereof. A preferred group of chain extending agentsincludes ethylene glycol, 1,4-butanediol, diethylene glycol, orpropylene glycol. Other chain extenders include primary and secondarydiamines which react more readily with the polyisocyanates of theinstant invention than does water. These include phenylenediamine,ethylenediamine, diethylenetriamine, N-(2-hydroxypropyl)ethylenediamine,N,N'-di(2-hydroxypropyl)ethylenediamine, piperazine, 2-methylpiperazine.The chain extender is preferably present in amounts from 2.0 weightpercent to 10 weight percent, more preferably from 4.0 weight percent to7.0 weight percent.

Any suitable catalyst may be used including tertiary amines such as, forexample, triethylenediamine, N-methylmorpholine, N-ethylmorpholine,diethylaminoethanol, N-lauryl morpholine,1-methyl-4(dimethylaminoethyl)piperazine,3-methoxy-N,N'-dimethylpropylamine, N,N,N'-trimethylisopropyl propylenediamine, N,N,N,N'-tetraethylpropylenediamine, dimethylbenzylamine,mixtures thereof and the like. Examples of such commercially availablecatalysts are the DABCO® catalyst series available through Air ProductsCorp. Other suitable catalysts are, for example, tin compounds such asstannous chloride, tin salts of carboxylic acids, such as dibutyl tindi-2-ethylhexanoate and stannous octoate, available under the FOMREZ®trademark, and other organic metallic compounds such as are disclosed inU.S. Pat. No. 2,846,408. The amount of catalyst is preferably from 0.01weight percent to 2.0 weight percent based on the weight of the resincomponent.

A surface active agent is generally necessary for production of integralskin polyurethane foam having a well-defined pore-free skin and asuitable well-formed open-celled core. Numerous surface active agentshave been found satisfactory, such as those which aid in homogenizingthe starting materials, regulate cell structure, and/or act as wettingagents. Nonionic surfactants are preferred. Of these, the nonionicsurface active agents prepared by the sequential addition of propyleneoxide and then ethylene oxide to the propylene glycol and the solid orliquid organo silicones have been found particularly desirable. Examplesinclude siloxane oxyalkylene heterol polymers and other organicpolysiloxanes, oxyethylated alkyl phenol, oxyethylated fatty alcohols,paraffin oils, castor oil ester, phthalic acid esters, ricindolic acidester, and Turkey red oil, as well as cell regulators such as paraffins.Other surface active agents which are operative and include polyethyleneglycol ethers of long chain alcohols, tetra amine or alkanol amine saltsof long chain alkyl acid sulfate esters, alkyl sulfonic esters, andalkyl arylsulfonic acids.

A long chained branched and/or unbranched aliphatic composition havingfrom about 6 to about 20 carbons, preferably 10 to 15 carbons, may beused according to the present invention as a surfactant/wetting agenteither in addition to the above mentioned surfactants or as thesurfactant of the foam system. Alcohols of this type are known to thoseskilled in the art. The types of alcohols contemplated are commonlyproduced by hydroformylation of an olefin in the presence of a catalystsuch as a cobalt known as the oxo process. The preferred carbon rangefor use as a surfactant is from C₁₂ -C₁₅, although other low carbonalcohols in the plasticizer range are also useful. Examples of suitableoxo-alcohols include lin C₁₂ -C₁₃, lin C₁₃ -C₁₅, lin C₁₂ -C₁₃ -C₁₄ -C₁₅,and lin C₁₄ -C₁₅. The oxo-alcohols are typically supplied as isomericmixtures, these being suitable for use in the invention. Longer chainedalcohols are made by ethoxylating shorter chained alcohols and mayoptionally comprise ethylene oxide-propylene oxide adducts of theshorter chained alcohols. Examples of some commercially availableproducts include LIAL 125 from Enichem Augusta Spa or NEODOL® 25produced by Shell. The alcohol composition is preferably present inamounts of from 0.3 to 1.0 weight percent.

The main blowing and density controlling agent used according to thepresent invention is water. For the purpose of the invention, water ispresent in amounts effective to make a part having the desired density,for example, up to and including 2.0 pbw based on the total weight ofthe resin component for most applications. It is preferably present inamounts from about 0.4 weight percent to 1.0 weight percent based on thetotal of the resin component. The phrase "water-blown" is meant toexclude any other blowing agent besides water. Although water ispreferably the sole blowing agent used in the present invention, otherblowing agents may be admixed with water, including reactive blowingagents such as formic acid or tertiary alcohols, or physically activeblowing agents such as the volatile hydrocarbons and fluorocarbons,especially those fluorocarbons having an ozone depletion potential of0.05 or less, in which case the foam is referred to for purposes of thisinvention as a "polyurethane integral skin foam blown with water."

Additives may optionally be used in the process of the present inventionand include known pigments such as carbon black, dyes, and flameretarding agents (e.g., trischloroethyl phosphates or ammonium phosphateand polyphosphate), stabilizers against aging and weathering,plasticizers, such as gamma butyrolactone, fungistatic andbacteriostatic substances, and fillers.

The water-blown polyurethane system is run at an index of 60 to 150,preferably 90 to 115, more preferably 95 to 105, most preferably at 100.The index of the system is defined as the NCO/active hydrogen ratioequivalent multiplied by 100. In calculating the quantity of activehydrogens present, all active hydrogen-containing compounds other thannon-dissolving solids are taken into account, including polyols, chainextenders, functional plasticizers, etc.

The mechanical parameters of the instant process are flexible and dependon the final application of the integral skin polyurethane foam. Thereaction system is versatile enough that it may be made in a variety ofdensities and hardnesses. The system may be introduced into a mold in avariety of ways known to those skilled in the art. It may be shot into apreheated closed mold via high pressure injection technique. In thismanner, it processes well enough to fill complex molds at low molddensities (from 20 pcf to 40 pcf, preferably from 25 pcf to 32 pcf). Itmay also be run using a conventional open mold technique wherein thereaction mixture or system is poured or injected at low pressure oratmospheric pressure into a preheated open mold. In the instant process,the system may be run at mold temperatures from about 85° F. to about135° F. with from about 115° F. to about 135° F. being preferred.Depending on the shape and complexity of the part to be molded, the moldmay be rotated from 0° to 90° off of the horizontal axis using gravityto reduce skin defects, promote even flow, and promote a more uniformcell structure.

The water-blown integral skin foams of the present invention may be usedas steering wheels and preferably possess the following mechanicalproperties at overall molded densities from 25-45 pcf, preferably 25-35pcf, more preferably from 28-31 pcf, and optionally at skin thicknessesadvantageously 0.1 inch or less, more preferably less than 0.08 inch;skin and core tensile strengths of 400 psi or more, more preferably 500psi or more; skin and core split tear strengths of 18 pi or more, morepreferably 20 pi or more; skin and core Graves tear strength of 50 pi ormore, more preferably 70 pi or more; skin and core elongation of 140percent or more, more preferably 190 percent or more, and a compressionset of 30 percent or less, more preferably 25 percent or less, mostpreferably 18 percent or less. The thickness of the skin may becontrolled in part by reducing the number and/or size of the vent holesin the mold as discussed below. It was surprising to find that even atskin thicknesses of 0.1 inch or less, the skin formed using the rawmaterials of the invention is free of surface defects such as poreformation, bubbles, and skin delamination; and the skin has highstrength and exhibits a taber abrasion loss of less than 200 mg.

Another feature of the invention allows one to utilize a mold with fewervent holes, resulting in raw materials savings. A typical steering wheelmold has from 8 to 20 vent holes depending on the size and complexity ofa CFC-blown integral skin part. The vent holes serve to preventexcessive pressure buildup and poor skin formation and aid in the flowof material through complex shapes by allowing volatized blowing agentand urethane to escape through the hole. Without vent holes or with aninadequate number of vent holes, the trapped gases will form bubblesnear the surface of the skin. To compensate for the raw material lostthrough the vent holes, anywhere from 25 to 75 weight percent excess ofraw material is shot into the mold resulting in higher costs per partthan would otherwise be necessary.

In the water-blown polyurethane system of the present invention, thelower molecular weight of water requires less water on a weightpercentage to produce the same number of moles as CFC. It has beenfound, however, that using molds having the same number and size of ventholes suitable for use in CFC-blown systems produced a part with asubstandard skin delaminating from the core, referred to as theformation of "onion skin." Without being bound to a theory, it isbelieved that this effect is due, at least in part, to an excess ofcarbon dioxide and raw material escaping through the vent hole with alarge enough pressure drop within the mold to interfere with asatisfactory densification of raw material at the mold surface. It wouldseem that the pressures generated within the mold by the blowing actionof carbon dioxide are not sufficient to solubilize that gas at thesurface of the mold. By reducing the number of vent holes, the pressurewithin the mold is increased, possibly increasing the solubility of thegas in the raw material at the surface of the mold rather than escapingout of the raw material through the vent holes.

To make a good quality skin free of bubbles, pores, and which adhereswell to the core, the number or number and size of the vent holes in themold are reduced with the added advantage of reduced raw material waste.Thus, the amount of water-blown overall raw material needed to produce apart having a density equivalent to a part blown with a physicallyactive blowing agent is reduced by approximately 10 weight percent toabout 20 weight percent, the exact percentage reduction varying with theparticular density of the part and complexity of the mold. For example,in a steering wheel mold which has 12-16 vent holes and requires 850grams of raw material to make a 25-30 pcf part, only 4 or 5 vent holesof reduced size are required to make a water-blown part of comparabledensity using 750 grams of raw material.

The following examples are offered to illustrate various aspects of theinvention. Those skilled in the art will appreciate that they are notlimiting to the scope and spirit of the invention and various andobvious modifications will occur to those skilled in the art.

Polyol A is an all propylene oxide adduct of propylene glycol having anominal hydroxyl number of 29.

Polyol B is a propylene oxide-ethylene oxide adduct oftrimethylolpropane having a nominal hydroxyl number of about 26.6 and anaverage functionality of about 2.2.

Polyol C is a 66.7 part by weight Polyol B and a 33.3 part by weightPolyol A blend having about a 4.8 weight percent ethylene oxide cap anda nominal hydroxyl number of about 27.4.

Polyol D is a propylene oxide-ethylene oxide adduct oftrimethylolpropane having a 13 weight percent ethylene oxide cap, anominal hydroxyl number of about 35, and an average functionality ofabout 2.6.

Polyol E is Polyol D as a carrier for a graft polyol containing 31weight percent of 1:1 acrylonitrile:styrene, the graft polyol having anominal OH of 24.

Polyol F is a propylene oxide-ethylene oxide adduct oftrimethylolpropane having about a 15 weight percent ethylene oxide cap,a nominal hydroxyl number of 25, and an average functionality of about2.3.

Polyol G is a propylene oxide-ethylene oxide adduct of glycerine havingan 18.5 weight percent ethylene oxide cap, a nominal hydroxyl number of35, and an average functionality of about 2.6.

Polyol H is a 77/23 weight percent blend of Polyol E and Polyol D,respectively, having a nominal hydroxyl number of 26.7.

Polyol I is a propylene oxide-ethylene oxide adduct of glycerine havinga 16.5 weight percent ethylene oxide cap, a nominal hydroxyl number of35, and an average functionality of about 2.6.

Polyol J is a propylene oxide-ethylene oxide adduct of glycerine havinga 21 weight percent ethylene oxide cap, a nominal hydroxyl number of27.5, and an average functionality of about 2.5.

Polyol K is a propylene oxide-ethylene oxide adduct of dipropyleneglycol having an 18 weight percent ethylene oxide cap, a nominalhydroxyl number of 56, and an average functionality of about 2.9.

Polyol L is a propylene oxide adduct of a glycerine/propylene glycolblend having a nominal hydroxyl number of 57.6 and an averagefunctionality of about 2.7.

Isocyanate A is a 98 weight percent 4,4'-diphenylmethane diisocyanatehaving 2 weight percent of other MDI isomers, an NCO content of 33.6weight percent, and a functionality of about 2.

Isocyanate B is a uretonimine-carbodiimide-modified 4,4'-MDI containingabout 75 weight percent 4,4'-MDI and 25 weight percent of auretonimine-carbodiimide-modified 4,4'-MDI, having an NCO content ofabout 29.5 weight percent.

Isocyanate C is a urethane-modified diphenylmethane diisocyanatecontaining 50 weight percent of quasi-prepolymer, the remainder beingessentially 4,4'-MDI.

Isocyanate D is a polyphenylene polymethylene polyisocyanate having afunctionality of approximately 2.7.

Isocyanate E is a diphenylmethane diisocyanate composition containingabout 50 weight percent 2,4'-MDI, the remainder being essentially4,4'-MDI.

Ethylene Glycol, Diethylene Glycol, and Glycerine are chain extenders.

DABCO XFE 1027 is an amine used as a delayed action gel available fromAir Products.

DABCO BL-11 is a 70 percent Bis(dimethylaminoethyl)ether; 30 percentdipropylene glycol (DPG) blowing catalyst available from Air Products.

DABCO BL-17 is a delayed action acid blocked version of DABCO BL-11,used as a blow catalyst, and available from Air Products.

DABCO HE is an amine catalyst providing delayed cream or faster demold,available from Air Products.

DABCO DC-1 is a delayed action amine-based gel catalyst available fromAir Products.

DABCO 8154 is a delayed action acid blocked version of a 33 weightpercent TEDA solution in dipropylene glycol available from Air Products.

UL-1 is an organotin catalyst available from WITCO Corp.

OXO-ALCOHOL is Lial 125, a linear C₁₂ -C₁₅ alcohol composition availablefrom Enichem Agusta.

X2-5384 is a silicone super wetting surfactant available from AirProducts.

Uvinul A03 is an anti-oxidant available from BASF Corp.

Givsorb UV-1 is an ultraviolet stabilizer available from Givaudan Corp.

Gamma Butyrolactone is a plasticizer available from BASF Intermediates.

I-460 is a 75/25 weight percent BDO and TEDA, respectively, amine gelcatalyst available from BASF Corp.

Tegostab B-2219 is a silicone cell stabilizing surfactant available fromGoldschmidt.

TEST METHODS

Density ASTM D-1622

Tensile Elongation ASTM D412 Die A

Split Tear ASTM D-1938

Graves Tear ASTM D-412 Die C

Shore Hardness ASTM D-2240

Compression Set ASTM D-3574

Quasi-prepolymer 1

To a clean, dry, nitrogen-purged reactor is charged with about 54.5weight percent molten Isocyanate A, about 21.6 weight percent IsocyanateB, and 0.003 weight percent benzoyl chloride. The ingredients areagitated under a nitrogen blanket throughout the reaction. The reactantsare heated to about 60° C., after which about 23.9 weight percent ofPolyol A is added at a constant rate over a one-hour period of time. Thereaction is continued for the next three hours at 60°-65° C. and thencooled. The quasi-prepolymer had an NCO content of 24 weight percent anda viscosity of 120 cP at 25° C.

Quasi-prepolymer 2

The same procedure used to prepare Quasi-prepolymer 1 was employed inthe preparation of Quasi-prepolymer 2, except that the new amounts were65.3 weight percent of Isocyanate A, 5.9 weight percent of Isocyanate B,and about 28.8 weight percent of Polyol C instead of Polyol A. Thequasi-prepolymer had an NCO content of 23 weight percent and a viscosityof 154 cP at 25° C.

Quasi-prepolymer 3

The same procedure followed to prepare Quasi-prepolymer 1 was employedexcept that the new amounts were 65.4 weight percent of Isocyanate A,5.9 weight percent of Isocyanate B, and 28.6 weight percent of Polyol A,and the reactants were heated for two hours at about 80° C. after thePolyol was added.

The quasi-prepolymer had an NCO content of about 23 weight percent and aviscosity of about 143 cP at 25° C.

Quasi-prepolymer 4

To a clean, dry, nitrogen-purged reactor was added 61.104 weight percentmolten Isocyanate A, 24.254 weight percent Isocyanate B, and 0.003weight percent benzoyl chloride and agitated under a nitrogen blanket at50°-60° C. To the mixture was added a polyol blend comprising 9.760weight percent Polyol A and 4.879 weight percent dipropylene glycol at aconstant rate over a one-hour period of time. The reactants were heatedat 60° C. over the next two hours. The quasi-prepolymer had an NCOcontent of about 24.2 weight percent and a viscosity of about 246 cP at25° C. The dipropylene glycol raised the viscosity by about 100 cP overQuasi-prepolymers 1, 2, and 3.

Quasi-prepolymer 5

The same procedure as used in Quasi-prepolymer 4 was employed exceptthat the new amounts were 61.296 weight percent Isocyanate A, 24.331weight percent Isocyanate B, 9.34 weight percent Polyol A, and 5.03weight percent dipropylene glycol. The quasi-prepolymer had an NCOcontent of 24.2 weight percent and a viscosity of about 250.

Quasi-prepolymer 6

The same procedure as in Quasi-prepolymer 4 was followed, except using90.0 weight percent Isocyanate B, 6.5 weight percent Polyol A, 3.5weight percent dipropylene glycol, and seven (7) drops of benzoylchloride. The quasi-prepolymer had an NCO content of 24.3 weightpercent, a viscosity of 378 cP at 25° C., and was stored stable at 10°C. for a period in excess of three (3) weeks without crystallineformation.

Comparative Isocyanate 7

This isocyanate is a 50/50 blend of Isocyanate C and Isocyanate B,respectively, having an NCO content of about 26 weight percent.

Comparative Quasi-prepolymer 8

This isocyanate is a blend of about 78 weight percent Isocyanate C,about 16 weight percent Isocyanate D, and about 6 weight percentIsocyanate E.

Comparative Isocyanate 9

To a clean, dry, nitrogen-padded placed reaction vessel was charged 74.2weight percent Isocyanate C, 15.4 weight percent Isocyanate D, and 5.4weight percent Isocyanate E. The ingredients were blended at 25° C.±3°C. until homogeneous, after which 5.0 weight percent Freon-113 wascharged and blended at 25° C. until homogeneous. The blend had an NCOcontent of about 23.7 weight percent.

I-Skin Foam Samples 1-5

Foam Sample 1 was made by reacting Quasi-prepolymer 1 with the resincomponent in the proportions indicated on Table 1 below. The resincomponent ingredients were combined according to the type and amountsstated in Table 1 below and mixed at 2,340 rpm using a 3" mixer bladefor ten seconds at each successive addition of ingredients until allingredients were added. Once the resin was mixed, it was shot into aCannon L-mixhead and impingement mixed at 180 bar with Quasi-prepolymer1 and shot into an 8"×8"×2" open preheated mold at about 220 gpsthroughput. The mold was closed and clamped while the system foamed. Thepart was demolded and submitted for testing, the results of which arereported in Table 2. The same procedure was followed to prepare FoamSamples 2-5, except that Sample 2 using Quasi-prepolymer 3 was run on aPU-15 machine.

                                      TABLE 1                                     __________________________________________________________________________    FOAM SAMPLE       1      2     3*    4     5*                                 __________________________________________________________________________    QUASI-PREPOLYMER 1                                                                              63.1                                                        QUASI-PREPOLYMER 3       63.1                                                 ISOCYANATE 7                   58.8                                           ISOCYANATE 8                         61.6                                     ISOCYANATE 9                               46.3                               POLYOL D                                   48.03                              POLYOL E                                   22.42                              POLYOL F                                   11.70                              POLYOL G          60.98        60.98 60.98                                    POLYOL H          28.95        28.95 28.95                                    POLYOL I                 79.71                                                POLYOL E                 10.0                                                 ETHYLENE GLYCOL   4.74   5.9   4.74  4.74                                     DIETHYLENE GLYCOL 2.11         2.11  2.11                                     GLYCERINE                                  .48                                XFE 1027          0.63         0.63  0.63                                     I-460                                      1.00                               DABCO BL-17              0.1                                                  DABCO BL-11       0.32         0.32  0.32                                     DABCO HE                 1.30                                                 DABCO DC-1                                 0.14                               DABCO 8154                                 0.10                               UL-1              0.05         0.05  0.05                                     OXO-ALCOHOL       0.63   0.6   0.63  0.63                                     X 2-5384          0.21   0.5   0.21  0.21                                     TEGOSTAB B-2219                            0.09                               UNIVUL A03        0.35         0.35  0.35                                     GIVSORB UV-1      0.18         0.18  0.18                                     WATER             0.85   0.75  0.85  0.85                                     FREON F-11A (INHIBITED)                    10.49                              GAMMA BUTYROLACTONE      2.0                                                  FOMREZ UL-24             0.04                                                 RESIN TOTAL       100    100   100   100   100                                MIX RATIO (RESIN/ISO PBW)                                                                       100/63.1                                                                             100/63.1                                                                            100/58.8                                                                            100/61.6                                                                            100/46.3                           PROCESING DATA                                                                GASSING, BUBBLES, LITTLE TO                                                                            SOME  YES   YES                                      POROSITY          NONE                                                        DEMOLD TIME (SECONDS)                                                                           100    150   210   180                                      MOLD TEMPERATURE (F.)                                                                           125    115   105   115                                      TANKS (RESIN AND ISO)                                                                           75#-95#F                                                                             75#-95#F                                                                            75#-95#F                                                                            75#-95#F                                                                            70#-80#F                           __________________________________________________________________________     *COMPARATIVE                                                             

                  TABLE 2                                                         ______________________________________                                        SAMPLE       1       2       3*    4*    5*                                   ______________________________________                                        DENSITY      30      30.4    26    27    29                                   (OVERALL                                                                      MOLDED)                                                                       SHORE A      55      52      60    70    72                                   HARDNESS                                                                      AFTER 5      56      49      51    69    69                                   SECONDS                                                                       SKIN THICKNESS,                                                                            0.06    0.06                0.116                                IN.                                                                           TENSILE, P.S.I.,                                                                           608.5   656     365   422   857                                  SKIN                                                                          SKIN AND CORE                                                                              524.5   509           333   510                                  CORE         226.3   324     202   221   219                                  SPLIT TEAR, P.I.,                                                                          29.3    24      28    20.1  27                                   SKIN                                                                          SKIN AND CORE                                                                              22.3    24            16.9  19                                   CORE         18      16.5    12    10    8                                    GRAVES TEAR, 98      101     56    69    99                                   P.I., SKIN                                                                    SKIN AND CORE                                                                              84.6    86.8          52    53                                   CORE         47.2    61.3    30    36    23                                   ELONGATION, %,                                                                             208     226.7   170   165   127                                  SKIN                                                                          SKIN AND CORE                                                                              203     203                 123                                  CORE         187     190     128   156   117                                  COMPRESSION  15.4    25.5    80    90    19                                   SET, %                                                                        Taber ABRASION                                                                             67      144                 69.3                                 (MG. LOSS)                                                                    ______________________________________                                         *COMPARATIVE                                                             

The results indicate that the quasi-prepolymers and resin componentsused in the present invention, Samples 1 and 2, yield a foam having goodoverall mechanical properties, including compression set, compared tothe CFC-blown Sample 5. The comparative foams made with the same resincomponent but differing isocyanates, Samples 3 and 4, exhibited poorcompression sets and somewhat lower mechanical properties in otherareas. The inventive Samples 1 and 2 with thinner skins also exhibitedcomparable mechanical properties to the Sample 5 CFC-blown systempreviously used to manufacture integral skin parts. In particular, thecompression set values are close to or exceed the CFC-blown system, andthe tensile strength, split tear strength, Graves tear strength, andelongation matches or exceeds the CFC-blown foam. Thus, the water-blownpolyurethane system employed in the present invention is a replacementfor CFC-blown foams in every respect.

The processing characteristics of Foam Samples 1 and 2 were alsosuperior to those of Samples 3 and 4 with respect to faster demoldtimes, higher limits on mold temperature, a wide range in tanktemperatures, and few, if no, bubbles or pores on the surface of theskin.

FOAM SAMPLE 6

In this test, a 34 pcf microcellular polyurethane 1" plaque was made byimpingement mixing 212.3 grams of Quasi-Prepolymer 2 with 353.7 grams ofa resin composition according to the procedure used to make Foam Samples1-5. The resin composition comprised 65.48 weight percent Polyol J, 10weight percent Polyol E, 16 weight percent Polyol K, 5 weight percentethylene glycol, 1.1 weight percent DABCO XFE-1027 catalyst, 0.5 weightpercent DABCO BL-17, 0.6 weight percent X2-5384 surfactant, 0.7 weightpercent oxo-alcohol, 0.02 UL-1 catalyst, and 0.6 weight percent water.The 1" plaque was tested for physical properties and the followingresults were obtained:

    ______________________________________                                        Shore A Hardness      50                                                      Tensile              560 psi                                                  Elongation           400 percent                                              Split Tear            42 pi                                                   Tabor Abrasion       157 mg/loss.                                             ______________________________________                                    

The physical data indicates that this water-blown integral skinpolyurethane molded article is also a useful alternative to CFC-blownintegral skin applications such as shoe soles.

We claim:
 1. A water-blown polyurethane integral skin foam having anoverall molded density from 25 pcf to 45 pcf and the followingproperties based on skin and core:A) a tensile strength of 400 psi ormore; B) a split tear strength of 18 pi or more; C) a Graves tearstrength of 50 pi or more; D) an elongation of 140 percent or more; and,E) a compression set of about 30 percent or less.
 2. The foam of claim1, wherein the density is from 25 pcf to 35 pcf.
 3. The foam of claim 2,wherein the compression set is less than 25 percent.
 4. The foam ofclaim 3, wherein the compression set is less than 18 percent.
 5. Thefoam of claim 3, wherein the foam has a tensile strength of 500 psi ormore, a split tear strength of 20 pi or more, a Graves tear strength of70 pi or more, and an elongation of 190 percent or more.
 6. The foam ofclaim 1, wherein the foam is a steering wheel.